Alkylation of metal salt of carboxylic acid



United States Patent Ofifice 3,198,136 Patented Get. 22, 1963 Virginia No Drawing. Filed June 23, 1961, Ser. No. 119,020 6 Claims. (Cl. 260-515) This invention relates to a process for alkylating a metallic salt .bf an aromatic carboxylic acid.

Alkylatio of aromatic hydrocarbons has been carried out in the past chiefly with catalysts of the Friedel-Crafts type such as sulfuric acid, hydrogen fluoride, aluminum chloride, and the like. This type of process causes alkylation to take place preferentially on an aromatic nucleus and suffers from the disadvantage that the reaction is very difiicult to control. The use or an alkali metal in alkylating the side chains of aromatic hydrocarbons has more recently been discovered. Alkylation has been eitected by the reaction of an olefinic hydrocarbon and an aromatic hydrocarbon in the presence of an alkali metal. For example, in US. Patent 2,448,641, a cyclic aromatic hydrocarbon, having at least two hydrogen atoms on a carbon atom which is directly attached by a single bond to a nuclear carbon atom, is reacted with a monoolefin at temperatures in the range of 150 to 450 C. at super atmospheric pressures of 503 000 atmospheres. Alkyla-tion in these instances takes place preferentially on the side chain and not on a nuclear carbon atom. Contrary to this, a process has now been discovered by which a metallic salt of an aromatic carboxylic acid can be alkylated on the aromatic ring in the presence of an alkali metal.

It is therefore an object of this invention to provide a process for alkylating metallic salts of aromatic carboxylic acids. It is a further object to provide a process by which a metallic salt of an aromatic carboxylic acid can be alkyla-ted-on a nuclear carbon atom of the aromatic ring in high yield. Still further objects will become apparent from the discussion which follows.

Accordingly, the above and other objects are accomplished by the provision of a process which comprises reacting a metallic salt of an aromatic carboxylic acid with an olefin in the presence of an alkali metal. The present process employs temperatures of from about 100 C to about 300 C. A preferred embodiment of this invention is the application of the above process to the alkylation of a metallic salt of benzoic acid. The most preferred embodiment of this invention is the process of alkylating sodium benzoate comprising reacting sodium benzoate with ethylene in the presence of sodium at between about 100 C to 300 C.

The process of this invention oilfers the advantage of a new route to obtain dibasic acids which are of commercial value. Over and above this definite advantage this process affords an economical and simple method of obtaining the valuable dibasic acids for commercial use.

The metal constituent of the metallic salts of the aromatic carboxylic acid reactant may be any metal M capable of being bonded to the carboxylic group via oxygen bonding of an aromatic carboxylic acid which is stable under thereaction conditions. However, the preferred metals which are a constituent of the metal salts employed as reactants are the group IA-IIA metals of the Periodic Chart of Elements, Fisher Scientific Company, 1959. The group IA metals include lithium, sodium, potassium, rubidium, cesium and francium while the group lIA metals include beryllium, magnesium, calcium, strontium and barium. The most preferred metal salts are those of the group IA metals as described hereinabove since they are most economical and more readily available. Of the group IA metal salts, those of sodium are most preferred.

The aromatic portion of the aromatic carboxylic acid salt reactant is an aromatic group containing up to 14 carbon atoms. Examples of such aromatic groups are aromatic radicals derived from benzene, naphthalene, anthracene, phenanthrene, fiuorcne, indene, isoindene and like substituted aromatic hydrocarbon ring systems containing 6 to 14 carbon atoms. It is preferred that the aromatic constituent be a mononuclear aromatic group.

The metallic salt of an aromatic carboxylic acid reactant of this invention can be any metallic salt of an aromatic mono or poly carboxylic acid. A typical example of a metallic salt of an aromatic mono carboxylic acid salt is sodium benzoate while a typical example of a poly carboxylic acid is the dis'odium salt of phthalic acid.

Thus, typical examples of metal salts of aromatic carboxylic acids used asreactants in this process are aluminum benzoate, cesium-l-naphthoate, the magnesium salt of l-naphthoic acid, calcium benzoate, barium benzoate, beryllium benzoate, the lithium salt of l-anthroic acid, the sodium salt of 4-indenoic acid, the lithium salt of l-fiuoric acid, the disodium salt of isophthalic acid, dipotassium salt of phthalic acid, the disodium salt of 1,4-dicarboxy naphthalene, and the like. The most preferred metallic salts of aromatic carboxylic acids used in this process are sodium benzoate, potassium benzoate, lithium benzcate, rubidium beuzoate and cesium benzoate since best results are obtained using these salts and they are more economical.

The olefin reactant of this invention is generally referred to as an alkylating agent. Accordingly, the alkylating agent used in this reaction can be any monoolefin or diolefin; however, the monoolefins are preferred, especially those containing up to 6 carbon atoms. Examples of such preferred alkylating agents are ethylene, propylene, butene-l, butene-Z, pentene-l, pentene-Z, hexene-l, hexene-Z, hexene-3, 4-methyl-pentene-1, S-methyl-but'ene- 1, 3-methyl-pentene-l, Z-ethyl butene-l, and the like. M'onoolefins having up to and including about 6 carbon atoms with the double bond in the terminal or alpha. position of a chain are most suitable. Especially preferred olefins in this invention are ethylene and propylene because of the facility with which they react and because of their low cost and abundance.

The alkali metals which can be used in this reaction are any of the alkali metals of group IA of the Periodic Chart of Elements, Fisher Scientific Company, 1959. These metals include lithium, sodium, potassium, rubidium and cesium. The most preferred alkali metal for this process is sodium because of its greater availability, reactivity, and enhanced yields obtained.

The alkylation reaction may be conducted either in the dry state or in the presence of an essentially inert solvent. Typical classes of solvents which may be used are the aliphatic hydrocarbons, tertiary amines, aliphatic ethers, cyclic ethers, and glycol ethers, and the like. Typical examples of glycol ether solvents are the diethers of diethylene glycol, triethylene glycol, tetraethylene glycol, dimethylene glygol, trimethylene glycol, tetramethylene glycol, etc. More specific examples of glycol others which can be employed are dimethyl ether of ethylene glycol, the ethylmethyl ether of diethylene glycol, the dimethylether of triethylene glycol, the dimethyl ether of tetraethylene glycol, dipropyl ether of tetraethylene glycol,

dibutyl ether of tetraethylene glycol, dimethyl ether of diethylene glycol, diethyl ether of diethylene glycol, dipropyl ether of diethylene glycol, dibutyl ether of dimethylene glycol, and the like. Typical cyclic ethers such as dioxane and tetrahydropyran may also be used. Typical examples of tertiary amines which can be employed are trimethyl amine, triethyl amine, tributyl amine, tripropyl amine, triisopropyl amine, tricyclohexyl amine, and the like. Typical examples of aliphatic solvents which may be used are hexane, heptane, nonane, and the like. The most preferred solvents are the cyclic ethers and aliphatic hydrocarbons such as tetrahydrofuran and nonane since they are more economical and best results are obtained using these solvents.

The ratio of alkylating agent to aromatic carboxylic acid salt can be varied over a wide range. Usually it is preferable to employ an excess over the stoichiometric amount of alkylating agent but in some cases it may be preferable to operate with a stoichiometric deficiency of alkylating agent. Hence, the molar ratio may vary (olefin to acid) from about 0.5 :1 to about 25:1. The preferred range (olefimacid) is from about 0.8:1 to about 15:1, although a ratio as high as 50:1 can be used if desired since excesses are readily recovered for reuse.

The ratio of alkali metal to aromatic carboxylic acid salt can also be varied over a wide range. The molar ratio may vary (alkali metal to carboxylic acid salt) from about 0.1:1 to about 3:1. The preferred range (alkali metal to carboxylic acid salt) is from about 0.821 to about 2:1.

Thus, in carrying out this invention one reacts, for example, sodium benzoate with ethylene in the presence of metallic sodium to obtain a mixture of alkylated substituted products. These products may then be oxidized and hydrolyzed to obtain polybasic acids, such as terephthalic acid, an important commercial compound.

The products obtained in the reaction of the metal salt of an aromatic carboxylic acid and an olefin in the presence of an alkali metal yields a mixture of alkylated aromatic carboxylic acid metal salts. The mixture of alkylated salts is very important chemical intermediates, hence the identification of each salt is not necessary. For example, in the above described reaction of sodium benzoate and ethylene in the presence of sodium the mixture of alkylated products obtained is essentially pethyl sodium benzoate, secondary butyl sodium benzoate and p-(3-methyl-3-pentyl) sodium benzoate. As will be seen in the working examples, the products of the process of this invention can be hydrolyzed and oxidized to obtain the corresponding polybasic acid. These acids can then be esterified and used as plasticizers, synthetic lubricants, and as ingredients in resins for fibers.

The process of this invention will be better understood by the following working examples. All parts are by weight unless otherwise specified.

Example I Alkylation of sodium benzoate.-Sodium benzoate (144 parts) and 23 parts sodium metal were placed in a ball mill under a nitrogen atmosphere. The mill was pressurized to 335 p.s.i. with ethylene, heated to 116 C., rotation commenced, and these conditions maintained for 6% hours. After the reaction was completed water was added incrementally to the product while under a nitrogen atmosphere. The water solution was filtered to remove insoluble impurities and concentrated by evaporation under vacuum to 99.7 parts. The concentrate was then acidified by the addition of concentrated hydrochloric acid. A yellow precipitate was formed.

A small sample of the precipitated product was esteritied with methyl alcohol and examined by vapor phase chromatography. The analysis indicated that the yellow precipitate contained a mixture of p-alkylated benzoic acid such as p-ethyl benzoic acid, p-secondary butyl benzoic acid, and p-(3-methyl-3-pentyl) benzoic acid.

Oxidation of the reaction product to terephthalic acid.- The acidified product was dissolved in an excess refluxing sodium hydroxide solution and oxidized by small additions of potassium permanganate until a pink color persisted. The excess permanganate was destroyed by the addition of 25 parts of ethanol. The reaction mixture was filtered to remove the manganese dioxide by-product which was washed with boiling water and the combined filtrates were acidified by the addition of hydrochloric acid. The white precipitate which was formed upon the addition of hydrochloric acid was filtered and dried. The dried precipitate was analyzed by infrared analysis giving bands at 11.4, 12.8 and 13.65 microns, indicating the white precipitate to be terephthalic acid. Esterification of a portion of the product with methyl alcohol was also accomplished by the addition of methyl alcohol to the acid product. The ester formed was analyzed by vapor phase chromatography which confirmed the infrared analysis identification of terephthalic acid.

Example 11 Alkylation of sodium benzoate-Sodium benzoate (144 parts) and 23 parts of metallic sodium were placed in a ball mill under a nitrogen atmosphere. 300 parts of tetrahydrofuran were added to the reactions. The ball mill was then pressurized to 335 p.s.i. with ethylene and heated to a temperature of 116 C., rotation commenced, and these conditions maintained for a period of 6% hours. After the reaction was complete, 1,500 parts of water were added incrementally to the reaction product while maintaining the mixture under a nitrogen atmosphere. The resultant solution was filtered to remove insoluble impurities and concentrated by evaporation under a vacuum to 99 parts. The solution was then acidified by the addition of concentrated hydrochloric acid to yield 76.7 parts of yellow precipitate.

Oxidation of the reaction product to terephthalic acid The acid product was dissolved in an excess refluxing sodium hydroxide solution and oxidized by small additions of potassium permanganate until a pink color persisted. The excess permanganate was destroyed by the addition of 25 parts of ethanol. The manganese dioxide byproduct was filtered and washed with boiling water and the filtrate acidified by the addition of hydrochloric acid. The white precipitate which was formed upon the addition of hydrochloric acid was filtered and dried. Esterification of a portion of the product with methyl alcohol was analyzed by vapor phase chromatography which indicated the white product from which the methyl ester was derived by the esterification to be terephthalic acid.

Example III Alkylation of sodium benzoate.Sodium benzoate (144 parts) and metallic sodium (23 parts) were placed in a ball mill under a nitrogen atmosphere. The mill was pressurized to p.s.i. with propylene and heated to a temperature of 138 C. for 6 /2 hours. To the reaction product, while under a nitrogen atmosphere, 1,000 parts of water were added. Insoluble impurities were removed by filtering and the filtrate was concentrated to 98 parts. The solution was then acidified by the addition of hydrochloric acid to yield a yellow precipitate. A sample of the product was esterified as in Example I and subjected to vapor phase chromatography analysis which showed the products to be essentially a mixture of alkylated benzoic acids which included isopropyl benzoic acid with some dimerized benzoic acids containing among other materials 4,4'-dicarboxy biphenyl present.

The esterified product mixture was oxidized and hydrolyzed in the same manner as set forth in Example I to obtain the dibasic acid products which were, as determined by infrared analysis, essentially terephthalic acid, phthalic acid and bibenzoic acid.

Example IV Alkylation of sodium benzate.Sodium benzoate (72 parts) and 3.9 parts of metallic potassium were placed in a ball mill under a nitrogen atmosphere. The mill was pressurized to 300 p.s.i. and heated to a temperature of 170 C. for 6% hours. After the reaction was complete water was added to the reaction product while under a nitrogen atmosphere. The water solution was filtered to remove insoluble impurities and concentrated by evaporation under vacuum. The solution was then acidified by the addition of concentrated hydrochloric acid and a yellow precipitate was formed.

Oxidation of the reaction product to dibasic acid. The acid product was dissolved in an excess refluxing sodium hydroxide solution and oxidized by small additions of potassium permanganate (80 parts) until the pink color persisted. The excess permanganate was destroyed by the addition of 25 parts of ethanol. The manganese dioxide by-product was filtered and washed with boiling water and the filtrate was acidified by the addition of concentrated hydrochloric acid to give a white precipitate. A portion of the white precipitate was esterified by the addition of methyl alcohol with sulfuric acid catalyst. The esterified product was analyzed by vapor phase chromatography which showed the acid product to be terephthalic acid.

Example V Sodium :benzoate (144 parts) and metallic potassium (39 parts) are reacted with propylene in dioxane at 160 p.s.i. for 7 hours at 110 C. in the same manner as set forth in Example II. Water is added to the reaction product while under a nitrogen atmosphere and the insoluble impurities are removed by filtration. The filtrate is concentrated by evaporation under vacuum and acidified; to give a precipitate. The products obtained are a mixture of alkylated benzoic acids.

This mixture of alkylated benzoic acids is oxidized and hydrolyzed in the same manner as set forth in Example H to obtain the corresponding dibasic acids including terephthalic, bibenzoic and phthalic acids.

Example VI Alkylation of potassium-1-naphth0ate.Potassium-1- naphthoate (210 parts) and 39 parts potassium metal in 140 parts of the dimethyl ether of diethylene glycol are placed in a ball mill under a nitrogen atmosphere and then pressurized to 350 p.s.i. with ethylene. The mixture is heated to 140 C. and the mill rotated for -a period of 6 hours. To the reaction product is added water in the same manner as set forth in Example II after which the solution is concentrated and acidified to obtain a good yield of alkyl-ated-l-naphtho-ic acids.

This mixture of alkylated naphthoic acids is then oxidized and hydrolyzed in the same manner as set forth in Example II to obtain dibasic acids in good yield.

Example VII Alkylation of calcium benz0ate.-Calcium benzoate (141 parts), 6.9 parts lithium metal and 168 parts of l-hexene are placed in a ball mill, heated to 160 C., and rotated for 10 hours. Water is carefully added to the reaction product while under a nitrogen atmosphere. The insoluble impurities are filtered and the filtrate concentrated under a vacuum after which said filtrate is acidified by the addition of hydrochloric acid to yield a yellow precipitate. The precipitated products that are obtained are a mixture of p-alkylated benzoic acids in good yields.

Example VIII Alkylation of calcium benzoate.-C-alcium benzoate taining nonane and pressurized to 1,500 p.s.i. with ethylene, the reactants being maintained at a temperature of 120 C. for a period of 5 hours. The water is added to the reaction products and the insoluble impurities are filtered 01f. The solution is concentrated under a vacuum and acidified with hydrochloric acid to obtain a precipitate which is a mixture of alkylated benzoic acids.

' This mixture of alkylated benzoic acids is then oxidized and hydrolyzed in the same manner as set forth in Example-IV to obtain the dibasic acids.

When the process is conducted in a dry state, the dry reactants are preferably ground up into fine particle size. The particle size of reactants is not critical but to enhance the speed of the dry reaction should average below about microns, preferably 50 microns. In general, the smaller the particle size the shorter the reaction periods required. Thus, best results are obtained when the average particle size of the reactants is less than about 10 microns. 'llhe smaller particle sizes facilitate handling and ease with which the reactor may be charged as well as assuring a homogeneous mixture before the reaction takes place.

When an inert diluent such as tetrahydrofuran is used in this alkyl-ation process, the solid reactants can be preground and premixed. However, the particle size of the reactants is not a critical feature of this invention.

The process of this invention can be run in a wide diversity of processing equipment and particularly excellent results are obtained in a pressure pot or autoclave equipped with a high speed stirrer. However, as indicated hereinbefore, a ball mill may be used.

In pregrinding, prem'ixing and in charging the processing equipment with the reactants, an inert gas is usually employed to prevent the reactants from coming into contact with air. Typical examples of the gases used are nitrogen, argon, krypton, and the like.

Generally, the temperatures employed in this invention range from about 100 C. to about 300 C. since within this temperature range fastest reaction rates are obtained and less undesirable side reactions occur. Lower temperatures can be employed although reaction rates are slower. Likewise, temperatures above about 300 C. are preferably avoided since some degradation may occur resulting in lower yields. The most preferred temperature range is from about C. to about C. since the process is more 'efficient within this range.

The reaction time for the alkylation process ranges from about 30 minutes to about 12 hours or longer. The preferred reaction time, however, ranges from about 1 hour to about 6 hours since better yields are obtained within this range.

This process is operable over a broad pressure range, depending upon the particular olefin being used and the temperature of the reaction. Thus, atmospheric and superatmospheric pressures can be used. However, generally the pressure ranges from about 25 p.s.i. to about 2,000 p.s.i. For best results, it is preferred that the pressure range from about 50 p.s.i. to about 1,500 p.s.i.

The alkylated metallic salts of the aromatic carboxylic acids of this invention, as was readily observed in. the specific working examples, are easily converted into the corresponding acids by various oxidation processes. These highly desirable acids, of which terephthalic acid is a prime example, are monomers well suited in the preparation of useful condensation polymers. For example, terephthalic acid may be produced by this process and used in the preparation of poly ester fibers and films (e.g., Dacron and terethylene fibers and Mylar and Cronar films). These acids or their esters may also be used as plasticizers for polyvinyl chloride, cellulose acetate, and the like.

Having thus described the unique processes for the alkylation of metallic salts of aromatic carboxylic acids, it is not intended that these processes be limited except as set forth in the claims.

I claim:

1. A process for alkylating a metal salt of an aromatic carboxylic acid wherein alkylation takes place on a nuclear carbon atom of the aromatic ring of said metal salt of an aromatic carboxylic acid, comprising reacting, in an inert medium, a metal salt of an aromatic carboxylic acid with an olefin having up to 6 carbon atoms and an alkali metal at a temperature of from about 100 C. to about 300 C. and at a pressure within the range of from about 25 p.s.i. to about 2000 p.s.i.; the molar ratio of said alkali metal to said metal salt of an aromatic carboxylic acid being within the range of from about 0.111 to about 3:1; the molar ratio of said olefin to said metal salt of an aromatic carboxylic acid being within the range of from about 0.521 to about 25:1; the metal constituent of said metallic salt of an aromatic carboxylic acid being selected from the group consisting of aluminum, alkali metals and alkaline earth metals; the nuclear carbon atoms of said metal salt of an aromatic carboxylic acid reagent having bonded thereto, in addition to the carboxylic group, only hydrogen atoms.

2. The process of claim 1 wherein said metal salt of an aromatic carboxylic acid is a metal salt of benzoic acid.

3. The process of claim 1 wherein said alkali metal is sodium.

4. The process of claim 1 wherein said metal salt of an aromatic carboxylic acid is sodium benzoate.

5. The process of claim 1 wherein said olefin is ethylene.

6. A process for alkylating sodium benzoate on a nuclear carbon atom of the aromatic ring of said sodium benzoatc, comprising reacting, in an inert medium, sodium benzoate with ethylene and sodium at a temperature of from about C. to about C. and at a pressure within the range of from about 50 psi. to about 1500 p.s.i.; the molar ratio of sodium to sodium benzoate being within the range of 0.8:1 to 2:1; the molar ratio of ethylene to sodium benzoate being within the range of from about 0.521 to about 25: 1.

References Cited in the file of this patent Benkeser et al.: Chem. Rev., vol. 57, August-December 1957, page 874. 

1. A PROCESS FOR ALKYLATING A METAL SALT OF AN AROMATIC CARBOXYLIC ACID WHEREIN ALKYLATION TAKES PLACE ON A NUCLEAR CARBON ATOM OF THE AROMATIC RING OF SAID METAL SALT OF AN AROMATIC CARBOXYLIC ACID, COMPRISING REACTING, IN AN INERT MEDIUM, A METAL SALT OF AN AROMATIC CARBOXYLIC ACID WITH AN OLEFIN HAVING UP TO 6 CARBON ATOMS AND AN ALKALI METAL AT A TEMPERATURE OF FROM ABOUT 100* C. TO ABOUT 300*C. AND AT A PRESSURE WITHIN THE RANGE OF FROM ABOUT 25 P.S.I. TO ABOUT 2000 P.S.I.; THE MOLAR RATIO OF SAID ALKALI METAL TO SAID METAL SALT OF AN AROMATIC CARBOXYLIC ACID BEING WITHIN THE RANGE OF FROM ABOUT 01:1 TO ABOUT 3:1; THE MOLAR RATIO OR SAID OLEFIN TO SAID METAL SALT OF AN AROMATIC CARBOXYLIC ACID BEING WITHIN THE RANGE OF FROM ABOUT 0.5:1 TO ABOUT 25:1; THE METAL CONSTITUENT OF SAID METALLIC SALT OF AN AROMATIC CARBOXYLIC ACID BEING SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, ALKALI METALS AND ALKALINE EARTH METALS; THE NUCLEAR CARBON ATOMS OF SAID METAL SALT OF AN AROMATIC CARBOXYLIC ACID REAGENT HAVING BONDED THERETO, IN ADDITION TO THE CARBOXYLIC GROUP, ONLY HYDROGEN ATOMS. 